class Solution {
public:
    int waysToStep(int n) {

        const int MOD = 1e9 + 7;

        if (n == 1 || n == 2)
            return n;
        if (n == 3)
            return 4;
        vector<int>dp(n + 1);

        dp[1] = 1;
        dp[2] = 2;
        dp[3] = 4;
        for (int i = 4; i <= n; i++)
        {
            dp[i] = ((dp[i - 1] + dp[i - 2]) % MOD + dp[i - 3]) % MOD;
        }

        return dp[n];
    }
};